Such a valve operating system is conventionally known, for example, from PCT International Patent Application Laid-open No. WO95/00959 and the like. In the valve operating system disclosed in that Patent Application, the armature is fixed to the upper end of the stem of the engine valve. In assembling the valve operating system to the cylinder head, the components disposed within the casing are assembled in sequence from the side of the cylinder head and finally, the casing is assembled to the cylinder head to cover these components. This assembling operation is carried out in a narrow space, and therefore the assemblability is poor.